1. Field of the Invention
The present invention generally relates to a technical field of mobile communications. More particularly, the present invention relates to a transport channel selecting apparatus and a transport channel selecting method for transmitting a predetermined combination of transport blocks of transport channels to a radio base station.
2. Description of the Related Art
In the technical field of the mobile communications, the IMT 2000 system has been developed as a next generation (third generation) mobile communications system and the IMT 2000 system is being standardized by 3GPP (3rd Generation Partnership Project) from requirements to realize high speed data communications that can provide mobile media services and to realize international global roaming services and the like.
FIG. 1 shows an overview of the mobile communications system. As shown in the figure, the mobile communications system 100 includes a user apparatus or a mobile terminal (UE) 102, a radio base station (or node B) 104 that communicates with the mobile terminal 102 by radio, a radio network control part (RNC) 106, and a core network (CN) 108 that communicates with the radio network control part 106 via wire lines. The radio network control part (RNC) 106 performs control of the radio base station 104, management of radio resources, control of hand over and the like. The core network 108 performs movement management of the mobile terminal 102, signaling, service control and the like. In the figure, Iu represents an interface between the core network 108 and the radio network control part 106, Iub represents an interface between the radio network control part 106 and the radio base station 104, and Uu represents an interface between the radio base station 104 and the mobile terminal 102.
From the viewpoint of protocol layers, the mobile communications system 100 is formed by, in an ascending order from the bottom layer, the physical layer (layer 1), the data link layer (layer 2) and the network layer (layer 3). Further, the layer 2 that mainly relates to operations of the radio network control part 106 includes a radio link control (RLC) layer and a medium access control (MAC) layer that is below the RLC layer. The RLC layer is for controlling operations of ARQ (automatic repeat request) and the like. Comminations between the layer 1 and the layer 2 are performed by “logical channel”, and communications between the layer 2 and the layer 3 are performed by “transport channel (TrCH)”. Such mobile communications system is disclosed in Japanese laid open patent application No.2003-46557 and “http://www.3 gpp.org/”, for example.
In the mobile communications system, the mobile terminal 102 and the radio base station 104 are connected by radio, and resources (bandwidth) used for the communications between them are limited to a predetermined range. In addition, for using resources efficiently and for transmitting high priority information rapidly, types of transport channels and the number of transport blocks (or number of ATM cells) are limited to a predetermined combination, so that the predetermined combination of transport blocks is transmitted to the radio base station. As the high priority information, there is a paging channel (PCH) for example. As other transport channels, there are a notification channel (BCH : Broadcast channel) for transmitting information on radio base stations such as frequencies used by the radio base station and the like, an uplink common channel (RACH : Random Access Channel), a downlink common channel (FACH : Forward Access Channel), and a dedicated channels (DCH) and the like. In the channels, the paging channel (PCH) and the downlink common channel (FACH) are multiplexed and transmitted in a predetermined channel (S-CCPCH : Secondary Common Control Physical Channel) from the radio base station.
FIGS. 2A and 2B show tables indicating examples of combinations of transport channels (TFC: Transport Format Combination) transmitted from the RNC to the node B. For the sake of simplicity, although seven combinations (TFC number 0-6) for four kinds of transport channels (TrCH_A-D) are shown in the tables, other values can be taken according to usage. Each line in the table shown in FIG. 2A indicates a combination of numbers of transport blocks for each of transport channels. For example, the combination indicated by the TFC number: 0 indicates that data of the transport channels TrCH_A-C are not transmitted but one transport block of a transport channel TrCH_D is transmitted. In addition, the combination indicated by the TFC number: 5 indicates that transport blocks of transport channels TrCH_A-D are transmitted by two, two, one and one respectively. By transmitting a predetermined combination of the transport blocks, resources can be used efficiently. The information relating to the predetermined combinations is stored n a memory as a TFC list table as shown in FIG. 2B. If a combination of transport blocks of transport channels that is not included in the predetermined combinations is transmitted to the node B, it is not guaranteed that data of the channels are properly transmitted (for example, unintentional coding process may be performed, or data of the channels may be discarded).
When the radio network control part RNC 106 sends data received from an upper part to the node B and to the mobile terminal UE, the radio network control part RNC 106 transmits transport blocks of transport channels to the node B according the above-mentioned predetermined combination. In this case, for transmitting transport blocks of transport channels in a transmission buffer to the node B, the radio network control part RNC 106 selects a combination and transmits transport blocks corresponding to the combination such that the best transmission efficiency can be obtained. Therefore, the radio network control part RNC 106 may select an optimal combination by checking all combinations shown in FIG. 2A.
FIG. 3 shows a conventional flowchart for determining a combination of transport blocks of transport channels. In step 302, transport blocks of transport channels to be transmitted to the node B are stored in the transmission buffer in the RNC, and a transmission request arises.
In step 304, the RNC accesses the TFC list table. In the TFC list table as shown in FIG. 2B, predetermined combinations of numbers transport blocks of transport channels are stored.
In step 306, the RNC selects a combination (TFC) from the TFC list table. The selected TFC is treated as a new TFC hereinafter.
In step 308, the RNC determines whether the new TFC can be used for the transmission request. For example, if the TFC number 4 (FIG. 2B) is selected and if transport blocks of transport channels TrCH_B-D are stored in the transmission buffer but data of the TrCH_A is not stored in the transmission buffer in step 308, the TFC number 4 cannot be selected since one transport block of TrCH_A must be transmitted according to the TFC number 4, so that the step goes to step 314. On the other hand, if transport blocks of the transport channels can be transmitted, the step goes to step 310.
In step 310, transmission efficiency is determined between an old TFC that was previously selected and the new TFC. The transmission efficiency is determined according to the numbers of transport blocks or information amount that can be transmitted by one time transmission. If the transmission efficiency of the new TFC is lower than that of the old TFC, the step goes to step 314. If the transmission efficiency of the new TFC is not lower than that of the old TFC, the step goes to step 312.
In step 312, the old TFC is updated to the new TFC. In step 314, it is checked whether every TFC has been checked. If there exists any unchecked TFC, the step moves to the step 304 so that the above-mentioned procedure is repeated. If every TFC has been checked, the step goes to step 316.
In step 316, the old TFC is determined as the combination used for actually transmitting the transport blocks of transport channels, and the transmission is performed and the process ends.
The above-mentioned series of operations generally need much amount of time, so that there is a problem in that real time processing becomes difficult and the transmission efficiency becomes worse due to increase of waiting time and delay time. In addition, if selection of a proper TFC is delayed, the status in the transmission buffer may be changed while selecting a TFC based on the status of the transmission buffer, so that the determined TFC may not be a optimum combination. As to the problems, in the invention described in the Japanese laid open patent application No.2003-46557, to improve the method of selecting a combination, various specific pieces of data such as list selection calculation data are generated and the specific pieces of data are compared each other so that a proper combination is selected. However, also according to this method, a proper combination needs to be selected by checking all combinations for transmitting given transport channels to the radio base station. Thus, since generation of the pieces of data used for comparison and the comparison of the pieces of data may be delayed, the above-mentioned method is not effective.